UC professor solves shattered sunroof problem

A San Jose woman had a frightening experience when her sunroof suddenly shattered above her head while she was driving. Michelle Park asked BMW to cover her sunroof under warranty but the carmaker refused. That's when 7 On Your Side got involved.

Park vividly remembers what happened that early Saturday morning. She says she was driving northbound on Highway 101 just past Sunnyvale when she heard a loud bang.

"It was like a little mini-explosion going right above your head and then you think, 'Oh my God, what just happened,'" Park said.

The explosion left a huge hole in her sunroof. Only the jagged edges remain.

"I looked around, looked through my rear view mirror saw that all my windows were intact, nothing had shattered so I pulled back the cover of my sunroof and shattered glass started falling on me," Park said.

Park brought her new 2010 328i into Stevens Creek BMW in Santa Clara for inspection. The service manager wrote in an email to BMW corporate saying, "The shop foreman found no signs of impact damage. The client is requesting this to be repaired under warranty."

An hour later, BMW replied saying, "I have picked up more rocks in the last three months and this is not a product issue. She will need to contact her insurance company."

"He should have requested for pictures, he should have said, he'll send somebody out to inspect it, that was it, in 3 minutes he said it was a rock issue, how would he know," Park said.

Park searched the internet and found that car owners of various makes reported their sunroofs also suddenly shattered.

7 On Your Side talked to Stevens Creek BMW. Officials there declined to go on camera, but said a rock likely hit the window and bounced back on the road.

7 On Your Side then discussed this incident with Tarek Zohdi, a professor of mechanical engineering at UC Berkeley. He calculated a rock lofted into the air by a vehicle tire would reach a height of 10-15 feet and would have to come down at 70-80 miles an hour to break the sunroof.

"There is not a chance in the world that an unintentional rock that is lofted by a vehicle would ever break a sunroof panel," Zohdi said.

Zohdi says the maximum velocity of a rock coming down would be 25 miles an hour, well short of the needed 70 miles an hour. He said it is more likely the sunroof broke due to the stress caused by changes in temperatures or from fatigue.

"In both cases I would say in my opinion the car manufacturer has the problem; basically it's a manufacturers defect," Zohdi said.

7 On Your Side called BMW corporate. It agreed to replace the sunroof free of charge even before we informed it of the professor's finding.

Park is happy and so is BMW, saying, "We're pleased that everything has been resolved with Miss Park and that she's happy with the way things went with her car."

Tarek says it is possible a rock could break a windshield with a direct hit, but the same scenario is not true for a sunroof since the rock would have to be first lofted into the air.